Defects in photoreduction reactions: Fundamentals, classification, and catalytic energy conversion

Powered by optical energy, photocatalytic reduction for fuel production promises to be an ideal long-term solution to a number of key energy challenges. Photocatalysts with enhanced light absorption, fast electron/hole separation rates, and exposed activity sites are essential to improve photocatalytic efficiency. Semiconductors are constrained by their own intrinsic properties and have limited performance in photocatalysis, but defect engineering provides an opportunity to modulate the physical and chemical properties of semiconductors. Defect engineering has been shown to be effective in regulating electron distribution and accelerating photocatalytic kinetics during photocatalysis. This review introduces the definition and categorization of defects, then explains the main effects of defect engineering on photoabsorption, carrier separation/migration, and surface reduction reactions. We then review the milestones in the design of defect-engineered photocatalysts for key chemical reactions, including hydrogen evolution, CO2 reduction, and N2 reduction, and tabulate their respective effects on catalytic performance. Finally, we provide insights and perspectives on the challenges and potential of defect engineering for photoreduction reactions.